The present invention relates to an electron beam apparatus for making an inspection of a sample, such as a wafer, a mask, a reticle or a liquid crystal, for example, having a pattern with a minimum line width equal to or smaller than 0.1 μm formed thereon, with high throughput and high precision by irradiating an electron beam onto the sample, and also to a device manufacturing method using the same electron beam apparatus.
There has been well known such an electron beam apparatus that uses an electron beam in order to detect a defect on a sample, such as a semiconductor wafer or a mask, in a manner that a primary electron beam emitted from an electron gun is focused via an optical system into an image on the sample, secondary electrons emanating from the sample are detected to provide a secondary electron image, and finally the sample is evaluated based on thus obtained secondary electron image.
The method for irradiating the primary electron beam onto the sample in such an electron beam apparatus may include one method in which a multi-beam of primary electrons is formed and focused into an reduced image on the sample, while deflecting the multi-beam for scanning the sample surface or while providing the irradiation of the multi-beam across a relatively large area on the sample at once. The method for detecting the secondary electrons emanating from the scanned region or the irradiated region on the sample as the result of the electron beam irradiation includes one method using an image projection optical system which can provide a magnified projection image of the secondary electrons covering a relatively large area onto a detection surface so as to carry out the detection of the secondary electrons. In that detection method, for example, the secondary electrons are focused into an image in an entrance of a MCP or the like and converted to an optical signal by a scintillator or the like, and then an image of resultantly multiplied secondary electrons from the MCP is converted to an optical signal by the scintillator and guided onto a detector, such as a CCD, via a FOP (Filter Optic Plate), where the optical signal is converted to an electric signal to provide the secondary electron image.
The conventional electron beam apparatus as described above is, however, suffered from the following problems.
(1) When employing one type of optical system operable for converging both of the primary electron beam and the secondary electron beam simultaneously in an uniform magnetic field, there is a fear from the reason of a narrow beam spacing in the multi-beam used for the scanning operation that all of the secondary electrons forming a single secondary electron beam are not received in a single beam detector arranged for the detection of said secondary electron beam but a part of signal from said secondary electron beam could be get mixed onto any adjacent beam detectors.
(2) Although an electromagnetic lens of said image projection optical system normally produces a small magnitude of aberration along an optical axis, if the primary electron beam is deflected for the scanning over the sample, it could occasionally enter the lens at an angle in a position off from the optical axis, adversely enhancing the aberration. Further, the image projection optical system, if attempting to enlarge the field of view, could resultantly reduce transmission of the secondary electron and again adversely enhance the aberration. Further disadvantageously, the image projection optical system is likely to suffer from a problem of distortion that could be induced in association with a magnifying lens placed in a second and subsequent steps.
(3) Although some type of CCD implementing a surface detector may include an element having an exposure time as short as 5 μs, it is typically time-consuming when extracting data.
(4) From the fact that the spacing between the MCP and the scintillator may produce a blured beam on the order of 30 μm, it is required that a pixel on the sample should be enlarged sufficiently over said blur of 30 μm. To address this, it is required to employ an image projection optical system having an optical path as long as 1000 mm, but unfortunately the space charge effect from such a long optical path could adversely enhance the blur of the beam and the same image projection optical system is expensive, as well.
(5) The arrangement of the FOP and the CCD that have been optically adhered to each other makes the maintenance difficult.
(6) As for the irradiation optical system serving for irradiating an electron beam onto the sample, which is required to determine two different focal conditions, one for a crossover image and the other for a shaping aperture image, the system must have the optical path as long as 500 mm and ends up in an expensive system.
(7) For the case employing an immersion-type magnetic lens characterized by a reduced axial chromatic aberration as an objective lens, there has been no optical axis adjusting method developed for controlling a primary optical beam emitted from the field away from the optical axis so as to pass through an NA aperture. Therefore, it is difficult to reduce the aberration in the image projection optical system satisfactorily.
(8) There has been no method established for designing an objective lens comprising a deflection coil to satisfy the MOL (Moving Objective Lens) condition by using the immersion-type magnetic lens.
The present invention has been made in the light of the above lined-up current situations, and an object thereof is to provide an electron beam apparatus that can overcome the above problems.
Another object of the present invention is to provide a device manufacturing method directed to improve an inspection precision and throughput by using the above-designated electron beam apparatus to inspect a semiconductor device in the course of its manufacturing or as a finished product.